Rocket engines require propellants to be fed to them at very high pressures. This has historically been accomplished in two general ways: first, with the use of a pressurized fluid, such as high pressure helium; and second, with the use of a pump.
In the first way (e.g., a “blowdown” system), a pressurized fluid, such as helium, is added directly to the propellant tank and exerts a force on the propellant. The problem with this method, however, is that the pressurized fluid also exerts a force on the propellant tank. Because of the extremely high pressures required of the pressurized fluid, the walls of the propellant tank must be thick enough to withstand the pressure. The propellant tank is therefore very heavy. Rockets employing the pressurized fluid must use a greater proportion of their thrust lifting this extra weight, and therefore they are not as efficient as rockets that do not require this added weight.
Historically, one way to solve the above weight problem is with the use of a pump. Pumps (e.g., reciprocating, centrifugal, or radial pumps) are generally very complex and expensive and require their own driving means, such as an engine. Further, the engine driving the pump burns a significant percentage of the total propellant. For small rocket engine systems, since a pump is too complicated and too expensive, pressurized fluids are generally used to pressurize the propellant. However, for large rocket engine systems, pumps have the advantage that the walls of the propellant tank need not be thick, since there is little pressure in the tank. Therefore, the propellant tank is much lighter, and the added weight of the pump is more than offset by the reduction in propellant tank weight.
U.S. Pat. No. 3,213,804 to Sobey (“Sobey”) discloses fluid pressure accumulators that are connected to sources of low and high pressure by means of valves. Essentially, the pressurized fluid exerts force on the propellant in small, designated storage tanks. While the walls of these containers must be thick in order to withstand the high pressure of the pressurized fluid, the walls of the propellant tank need not be. Therefore, the total weight of the rocket engine system employing Sobey's invention may be less than that of the previously discussed rocket engine system because these storage tanks (fluid pressure accumulators) are small in comparison to the propellant tanks.
U.S. Pat. No. 6,314,978 to Lanning, et al. (“Lanning”) discloses a reciprocating feed system for fluids having storage tanks 1, 2, 3 that are similar in purpose to the fluid pressure accumulators disclosed in Sobey. Instead of valves 50, 52, 54 disclosed in Sobey, Lanning discloses four valves for each storage tank 1, 2, 3. For example, associated with storage tank 1 are: valve 13 between storage tank 1 and low pressure fluid 5; valve 16 between storage tank 1 and high pressure discharge 7; valve 20 between storage tank 1 and vent manifold 18; and valve 24 between storage tank 1 and pressurized gas supply 8. Each valve must be accurately and reliably controlled by a controller 11. Further, each valve may have an associated sensor 11a.